Conventionally, in order to provide the fiber to the home (FTTH) service which enables the optical communication between one transmitter station and a plurality of subscribers, a so-called passive optical network (PON) system in which the respective subscribers share one optical fiber by interposing a multiple-stage optical splitter has been realized. Nevertheless, the PON system entails technical problems such as congestion control and securement of a receiver dynamic range against the increase in transmission capacity in the future.
As one means for resolving the foregoing technical problems, migration to the single star (SS) system can be considered. Upon migrating to the SS system, since the number of fiber cores will increase on the station side in comparison to the PON system, realization of ultrafine and ultrahigh density optical cables is essential on the station side. As optical fibers for achieving such ultrafine and ultrahigh density optical cables, for instance, preferably used may be a multi-core fiber comprising a plurality of cores in a single clad.
As such multi-core fiber, for instance, the optical fiber disclosed in Patent Literature 1 includes seven or more cores disposed two-dimensionally in the cross section thereof. Moreover, for instance, Patent Literature 2 discloses an optical fiber in which a plurality of cores are arranged in parallel in a straight line, and describes that the connecting of the optical waveguide part and the semiconductor optical integrated element is facilitated.